To automatically weld two pieces of pipe together at a joint requires that the bevel of the joint be uniform. When the pipe is cut at 90.degree. to its longitudinal axis, the production of bevels at a constant angle is relatively simple. However, when the pipe is cut at an angle to form a mitered joint of, for example, 45.degree., the bevel must be uniform to produce a uniform groove for welding and the angle at which the bevel is cut must vary, since the mitered cut follows an eliptical path over the surface of the the pipe. The manner in which this bevel varies is defined by a complicated set of trigonometric equations.
There are many known devices in the prior art for cutting pipes and the like at the desired angle of cut and at different angles with selected bevels. For example, U.S. Pat. No. 4,143,862 and U.S. Pat. No. 4,216,945 both show an apparatus for automatically cutting a mitered cut at a varying angle of bevel by rotating the torch and driving mechanism around the pipe. A combination of two servo motors positions the cutting torch at a selected point on the surface of the pipe while an additional two servo motors set the angle that the torch makes with the surface of the pipe. A profile of the desired cut is required to be cut and attached to the pipe which, through the use of optical sensing devices, provides positional information to the servo motors. The mathematical equations defining the bevel angle are translated onto this profile in the form of a curve. This is a tedious process since each pipe needs a separate profile and, in addition, the profile must be applied to the surface of the pipe with due care.
The mathematical equations provide a mathematical relationship between the desired cut and the four controlling servo motors. The equations also take into consideration operator error in applying the profile since there is no feedback between the profile and actual cut. In addition, there is no provision for mating pipes of differing thicknesses.
A need has thus arisen for a mitered cutting system which utilizes a minimum number of servo motors to position the torch about the pipe and a method for accurately controlling the cutting operation. To accurately control the cutting operation, a comparison of the actual and desired cut is preferred in order to maintain a high level of quality control. The various characteristics defining any two intersecting pipes, such as the inner diameter and outer diameter of the pipes and the intersection angle thereof, need to be readily changable to accommodate a manufacturing environment.